Jennifer Lopez, 58, had jumped at the chance to get the Johnson & Johnson vaccine last March, but soon began feeling regret when data showed it might be less effective than other coronavirus vaccines.

So, when the Centers for Disease Control and Prevention signed off on booster shots Thursday night for all Johnson & Johnson recipients who had gone two months since their shot, Lopez wasted no time seeking one out.

“I’m actually on my way today to go get it,” the Paso Robles, Calif., woman said in an interview Friday morning.

Lopez was part of a throng of booster seekers, many of them recipients of the Johnson & Johnson vaccine, who rushed to get additional shots on Friday, just hours after federal officials cleared both the Johnson & Johnson and Moderna boosters. An estimated 70 million people who received vaccines in the U.S. are now eligible for all of the three authorized boosters, officials said. That includes most of the 15 million recipients of the single-dose Johnson & Johnson vaccine.

Many consumers were buoyed by the news that they could pick a booster different than their original brand, with some Johnson & Johnson recipients saying they coveted the added security of the Moderna or Pfizer-BioNTech vaccines, based on studies showing they offered greater protection. The Pfizer-BioNTech booster had already been authorized.

Others were confused by the so-called mix-and-match policy. Lopez, at heightened risk for severe infection because of her weight, among other issues, said she expected to get a second Johnson & Johnson shot. When a reporter told her she could choose any of the three boosters, she was surprised and relieved, saying she would prefer to get a different shot that offered more protection.

“I had a lot of regret about choosing J & J,” she said.

Erin Dwyer, 40, shared those sentiments, and began refreshing the CVS Pharmacy website to make an appointment to get a Pfizer BioNTech booster on Thursday night. At first, she saw an error message that said she was not eligible to get the messenger RNA vaccine, seven months after her Johnson & Johnson shot. She tried again in the early morning, and said the website crashed. She refreshed the page again and again, and eventually, snagged an appointment for Friday morning.

“Even the pharmacist was impressed,” said Dwyer, an associate professor of history at Oakland University near Detroit. “I was the first booster of the day.”

Bruce Nilles, 58, of Oakland, Calif., also scored an early shot. He made an appointment online at 6 a.m. and was in line for a Pfizer-BioNTech booster at his local Walgreens by 9:15 a.m. The pharmacist was still reading the CDC’s new guidance when Nilles walked up to the counter for his booster.

“He says, ‘I just printed off the memo, let me finish reading it,’ ” he said. Nilles got his booster a few minutes later.

Not everyone was successful amid foul-ups on the first day of the expanded rollout. Some providers had not yet been notified in the early morning that the Moderna and Johnson & Johnson boosters were cleared for use. And some large pharmacies were still updating their online appointment-making systems to accommodate the new policies.

When Bethesda, Md., attorney Brad Shear, 48, heard he was eligible for one of the mRNA boosters, he was eager to get another shot. Shear had received the Johnson & Johnson vaccine in the spring when the public health message was to “get whatever you can get,” he said Friday. But he grew increasingly nervous about the level of his protection as the months passed.

Shear scheduled an appointment Friday for 11:20 a.m. at a pop-up clinic in a Maryland suburb jointly run by the community and Giant Pharmacy. The clinic’s flier advertised several vaccines, including Pfizer-BioNTech boosters for those eligible. But pharmacy personnel took one look at his vaccination card and told Shear the state had not been authorized to give mix-and-match boosters.

“They turned me down!” Shear said. “This is insane.”

Around 10 a.m., Maryland officials emailed vaccine providers that they should make Moderna and Johnson & Johnson boosters available to eligible Marylanders, effective at 11 a.m., according to Maryland health department spokesman Andy Owen. Giant Food spokeswoman Felis Andrade said when the retailer booked the clinic with the community weeks earlier, only the Pfizer-BioNTech booster was approved, which the pharmacy agreed to provide.

Shear, meanwhile, tried again to book an online appointment, this time with CVS. Eventually, he was able to schedule an appointment on Monday night.

The new recommendations also confounded some people who say they want a booster, but aren’t sure which one they qualify for – or if they are eligible at all. “It is confusing,” said Stephanie Trell, who received the Johnson & Johnson shot.

Trell, 53, who lives in Manhattan and works in finance and marketing, said she did not know which booster she might be eligible to get. “I would love to get Moderna, but can I get the Moderna?” she asked.

Federal regulators allow mixing and matching of all three vaccines for all those eligible for boosters. All Johnson & Johnson recipients who are two or more months out from their shot can get any of the three available boosters. Booster eligibility for those who received the Moderna or Pfizer-BioNTech vaccines is limited to those six months out from their last shot, who are 65 or older, as well as those 18 or older at increased risk for serious disease because of underlying health conditions or because they live or work in settings that place them at higher risk of infection.

Some people who got Johnson & Johnson vaccines say they plan to stick with what’s familiar.

Sharon and Allan Frey, who live in a senior park in Apache Junction, Ariz., had no side effects from their first shots and don’t want to risk feeling ill after a booster.

“That was another reason that we wanted Johnson and Johnson,” Sharon Frey said. “A lot of the people in our park had gotten the other kinds (of vaccines), and they had fevers, they felt sick for a couple of days, and their arms swelled up or they had a sore arm … That doesn’t sound cool.”

The Freys, who are in their 70s, said they have been eagerly awaiting the Johnson & Johnson boosters, especially because they have seen few people in their high-risk community wear masks or practice social distancing in recent months. Some neighbors have even caught covid-19 after attending bingo or karaoke nights.

“I’m glad to see that they finally been approved,” Sharon Frey said.